Cut of piezoelectric oscillator, piezoelectric oscillator, and piezoelectric device

ABSTRACT

A cut of a piezoelectric oscillator uses a quartz plate having an electric axis, mechanical axis, and optic axis on an X axis, Y axis, and Z axis, respectively. An X′ axis is set by rotating the X axis with an angle of 3-30 degrees in a clockwise direction about the Z axis. A Z′ axis is set by rotating the Z axis in the clockwise direction with an angle of 33-36 degrees about the X′ axis. The quartz plate has sides parallel to the X′ axis and Z′ axis, respectively. Furthermore, the plate has sides parallel to X″ axis and Z″ axis, respectively, which have been rotated in the clockwise direction with angles of from −35 degrees to −2 degrees about a Y′ axis that is the thickness direction of the cut of the piezoelectric oscillator.

RELATED APPLICATIONS

[0001] This application claims priority to Japanese Patent ApplicationNo. 2003-076245 filed Mar. 19, 2003 which is hereby expresslyincorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates to a cut of an oscillator makinguse of a piezoelectric effect and, more particularly, to a cut of apiezoelectric oscillator, piezoelectric oscillator, and piezoelectricdevice using a so-called new cut quartz plate.

[0004] 2. Related Art

[0005] As various kinds of electronic devices have been advanced andcommunication systems have evolved in recent years, piezoelectricdevices typified by piezoelectric oscillators have been used frequently.Especially, quartz acting as a piezoelectric material has enjoyed wideacceptance in piezoelectric devices, because high frequencies areobtained and stable frequency characteristics are provided. AT-cutquartz plates (hereinafter simply abbreviated AT-cut plates) have beenused in piezoelectric devices for a long time because piezoelectricoscillators having stable frequency characteristics in a widetemperature range are obtained. Such an AT-cut plate has one sideparallel to the X axis and has been cut at a cut angle obtained byrotating the XZ-plane with 35.25 degrees in a clockwise direction (asviewed from the −X direction of the X axis to the +X direction) aboutthe X axis.

[0006] In recent years, however, as oscillators and so on have beenpacked at increasing densities, the operating temperatures have beenelevated. Also, it has become necessary to set the operatingtemperatures of the oscillators higher. Therefore, a double-rotationoscillator whose cut angles are rotated about two axes has been devisedinstead of the conventional AT-cut oscillator.

[0007] If a quartz plate (double-rotation substrate) cut out with cutangles rotated relative to two axes among the crystallographic axes(electric axis, mechanical axis, and optic axis) of quartz is used, ithas been theoretically demonstrated that the central temperature of thefrequency-temperature characteristics shifts to the higher temperatureside. In a temperature range of from −25° to +100° C., cut anglesproviding stable frequencies exist (for example, see Japanese Patent No.3,218,537).

[0008] The double-rotation substrate can provide stablefrequency-temperature characteristics in this way. At the same time,many spurious oscillations occur compared with the main oscillations.Many frequency jumps or resistance value increases occur due tomechanical oscillation coupling of spurious oscillations with the mainoscillations. Many of the spurious oscillations are contour oscillationsdepending on the longer or shorter sides of blanks or are modes ofcombinations of them. Accordingly, when a blank is designed, its shapemust be determined carefully such that no spurious oscillations existnear the frequency of the main oscillations.

[0009] The temperature characteristics of the double-rotation oscillatorare as shown in FIG. 3 when the frequency-temperature characteristics inthe temperature range from −25° C. to +100° C. of the oscillator aretaken which has rotated with 34.9 degrees about the X axis afterrotating 10 degrees about the Z axis, for example. In the figure, thedotted line indicate the frequency-temperature characteristics of theconventional AT-cut oscillator. It can be seen that the double-rotationoscillator shows more stable frequency-temperature characteristics inhigher temperature regions as compared to the AT-cut oscillator. In thisdouble-rotation oscillator, the frequency-temperature characteristicshave a point at which the gradient of the tangential line is 0 nearapproximately 25° C. in the case of the AT-cut. The temperature at thispoint is hereinafter referred to as the central temperature. Incontrast, the double-rotation oscillator has the phenomenon that thecentral temperature varies from 25° C. to 100° C. or higher depending onthe rotational angle φ.

[0010] The characteristics of the double-rotation oscillator describedso far are useful. However, more spurious oscillations (undesiredoscillations) having other modes of oscillations are produced than theconventional AT-cut oscillator. For example, contour oscillationsdepending on the longer and shorter sides of the blank vary in frequencydue to deviation in blank contour. Therefore, if the frequency comes tooclose to that of the main oscillations, both oscillations aremechanically coupled, causing jumps in the frequency of the mainoscillations or resistance increases. Similarly, in the temperaturerange of from −25° C. to 100° C. taken as operating temperatures,spurious oscillations occur at certain temperatures near the mainoscillations. This produces the phenomenon that the frequency of themain oscillations deviates or the resistance value increases. Similarphenomena are observed with AT-cut oscillators. Especially, in the caseof double rotations, these phenomena occur frequently. The presentinventors have investigated the cause using an analytical method knownas the finite element method.

[0011] As a result, we have found that the cause is the direction ofdisplacement of thickness shear oscillation that is the mainoscillation. The conventional AT-cut oscillator produces a thicknessshear oscillation whose direction of displacement is only in theX-direction. On the other hand, the direction of displacement of thedouble-rotation oscillator has all of the components of X, Y, and Z. Thephenomenon of a frequency shift or resistance increase caused byspurious oscillations is due to the fact that the main and spuriousoscillations have common displacement components and thus cause couplingof oscillations (resonance). That is, the main oscillations of theAT-cut oscillator couple with oscillations having only X-directiondisplacement components. However, the double-rotation oscillator hasdisplacement components of three directions and so there arises thepossibility that coupling with the majority of spurious oscillationsoccurs.

SUMMARY

[0012] The present inventors have calculated the displacement vector onthe surface of a double-rotation cut quartz blank, i.e., within theplane formed by the X′ axis and Z′ axis and produced a clockwisein-plane rotation about the Y′ axis such that the X″ axis extends alongthe direction of displacement vector. A new rectangular blank has beencut so that both sides are parallel to the resulting new X″ axis and Z″axis, respectively.

[0013] That is, the present invention provides a cut of a piezoelectricoscillator comprising a quartz plate made of a quartz having an electricaxis lying on an X axis, a mechanical axis lying on a Y axis, and anoptic axis lying on a Z axis, the plate having a side parallel to an X′axis established by rotating the X axis in a clockwise direction aboutthe Z axis with an angle of from 3 degrees to 30 degrees, the quartzplate further having a side parallel to a Z′ axis obtained by rotatingthe Z axis about the X′ axis in the clockwise direction with an angle offrom 33 degrees to 36 degrees. This cut of a piezoelectric oscillator ischaracterized in that the quartz plate has sides parallel to X″ axis andZ″ axis, respectively, which have been rotated with angles of from −35degrees to −2 degrees in the clockwise direction about the Y axis thatis the thickness direction of the cut of the piezoelectric oscillator.

[0014] In the cut of a piezoelectric oscillator according to the presentinvention, the frequency of the main oscillations is stable againstvarious shapes and hardly varies even if spurious oscillations comeclose to the main oscillations. The possibility that frequency jumps orresistance increases take place is low.

[0015] In the present invention, “clockwise direction about an axis” isa direction taken from the negative side to the positive side of theaxis. Accordingly, “clockwise direction about the Z axis” means“clockwise direction as viewed from the −Z direction to the +Zdirection”.

[0016] A piezoelectric oscillator according to the present inventionconsists of any one of the above-described cuts of a piezoelectricoscillator and can provide improved stability of frequency againstmachining errors of the longer and shorter sides of a blank. Inaddition, a piezoelectric oscillator having a stable frequency in a widetemperature range of from −25° C. to +100° C. is obtained.

[0017] Also, a piezoelectric device according to the present inventionis characterized in that it is fitted with the above-describedpiezoelectric oscillator. As a result, more machining errors aretolerated in mass production steps, and a stable frequency is obtained.Consequently, where the temperature range used is wide as in automobileparts, the frequency can be stabilized without the need of a temperaturecompensation circuit. The cost can be decreased by avoiding increases inthe number of components and number of manufacturing steps.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is an explanatory view of double-rotation cut anglesforming the basis of embodiments of the present invention.

[0019]FIG. 2 is an explanatory view of a cut angle according to anembodiment of the invention.

[0020]FIG. 3 shows the frequency-temperature characteristics of adouble-rotation oscillator with φ=10° and θ=34.9°.

[0021]FIG. 4 is a diagram illustrating the direction of displacement ofmain oscillations on the plane of the double-rotation oscillator.

[0022]FIG. 5 is a graph showing the relation between the rotationalangle φ about the Z axis and the deviation γ of displacement from thedirection of the longer sides.

[0023]FIG. 6 shows the relation between the Z side ratio and frequencyin a case where the direction of displacement is parallel to thedirection of the longer sides.

[0024]FIG. 7 shows the relation between the Z side ratio and frequencyin a case where the direction of displacement deviates 8 degrees fromthe direction of the longer sides.

[0025]FIG. 8 shows the relation between the Z side ratio and frequencyin a case where the direction of displacement deviates 16 degrees fromthe direction of the longer sides.

[0026]FIG. 9 is a frequency distribution of variations in mainoscillation frequencies of various shapes in a case where the directionof displacement is parallel to the direction of the longer sides.

[0027]FIG. 10 shows the frequency distributions of variations in themain oscillation frequencies of various shapes in the case where thedirection of displacement deviates 8 degrees from the direction of thelonger sides.

[0028]FIG. 11 shows the frequency distributions of variations in themain oscillation frequencies of various shapes in the case where thedirection of displacement deviates 16 degrees from the direction of thelonger sides.

[0029]FIG. 12 is a diagram showing the frequency-temperaturecharacteristics of a cut of a quartz oscillator according to theinvention under conditions of φ=10°, Ω=−8.0°, and θ=34.85°.

[0030] FIGS. 13(A) and 13(B) are explanatory views of a piezoelectricoscillator according to an embodiment. FIG. 13(A) is a cross-sectionalview taken along line B-B of FIG. 13(B), and FIG. 13(B) is across-sectional view taken along line A-A of FIG. 13(A).

DETAILED DESCRIPTION

[0031] The preferred embodiments of cut of a piezoelectric oscillator,piezoelectric oscillator, and piezoelectric device according to thepresent invention are described in detail with reference to theaccompanying drawings.

[0032]FIGS. 1 and 2 are views illustrating cut angles of quartz forobtaining a cut quartz oscillator that is a cut of a piezoelectricoscillator according to the present invention. In FIG. 1, three axes ofa quartz crystal 10 crossing perpendicularly to each other, i.e.,electric axis, mechanical axis crossing perpendicularly to the electricaxis, and optic axis crossing perpendicularly to those axes are taken asX axis, Y axis, and Z axis, respectively. With respect to the cut anglesof the double-rotation cut-angled quartz plate (quartz substrate) 11defined in the present invention, an X′ axis obtained by rotating the Xaxis about the Z axis with merely φ in a clockwise direction is firstestablished. The plate has sides parallel to the X′ axis. Furthermore,the quartz plate 11 has sides parallel to a Z′ axis obtained by rotatingthe Z axis in the clockwise direction with merely θ about the X′ axis.

[0033] A cut of quartz 12 according to the invention is a cut of quartzhaving sides parallel to an X″ axis and a Z″ axis obtained by rotatingthe quartz plate 11 about the Y′ axis with merely angle Ω as shown inFIG. 2. In this figure, +direction of the Y′ axis is a directiondirected from the rear surface of the paper to the front.

[0034] The present inventors have conducted various discussions on thecut angles of the quartz crystal 10 which have been rotated about the Xaxis, Z axis, and Y′ axis and have found that the present cut-angledoscillator suffers from less frequency jumps and resistance increasesdue to spurious oscillations in various forms than the conventionaldouble-rotation oscillator. Furthermore, the temperature characteristicsare more stable.

[0035] As shown in FIG. 4, the calculated result of the direction ofdisplacement of the main oscillations on the double-rotation cut quartz11 reveals that the direction of displacement of the main oscillationsis not parallel to the direction of the longer side on the X″ axis buthas a deviation angle γ as indicated by the arrow in the figure. FIG. 5shows the computationally derived results of the direction ofdisplacement of the main oscillations on the double-rotation cut quartz11 when the rotational angle φ about the Z axis is varied. The lateralaxis indicates the rotational angle φ about the Z axis, while thevertical axis indicates the deviation γ in the direction ofdisplacement. These are represented by defining the clockwise directionrelative to the +Y′ axis as positive (+). As can be seen from thefigure, as the rotational angle φ increases, the deviation γ between theX′ axis and the direction of displacement increases in one direction.

[0036] Accordingly, the blank is rotated about the Y′ axis within theplane formed by the X′ axis and Z′ axis with merely γ such that thedirection of the longer sides of the blank becomes parallel to thedirection of displacement of the main oscillations.

[0037] This rotational angle is Ω. For example, the degrees of thedeviation of the frequency of the main oscillations due to spuriousoscillations were calculated for a case where the direction ofdisplacement is parallel to the direction of the longer sides and for acase where the direction of displacement is not parallel. Also, thedegrees of increase in the resistance value were calculated. It is nowassumed that the sides parallel to the X″ axis are the longer sides andthat the sides parallel to the Z″ axis are the shorter sides. Theresults are shown in FIGS. 6-8. The lateral axis of each figure is the Zside ratio, i.e., the length of the shorter sides of the blank dividedby the thickness of the quartz. The vertical axis indicates thefrequency. Here, φ is 20 degrees, and the longer sides of the blank hasa constant length of 2.0 mm. In the figures, the frequency positions ofmain oscillations are indicated by the white dots. The frequencypositions of spurious oscillations are indicated by the black dot group.The size of each dot corresponds to the intensity of each oscillation. Alarger dot indicates a stronger oscillation. For example, the lines inFIG. 6 indicate the motion of a certain spurious oscillation. As the Zside ratio of the blank increases, the spurious position shifts to thelower frequency side. It can be understood, on the other hand, that themain oscillations are almost constant regardless of the Z side ratio andthat when the spurious oscillations are approached, the frequency shiftsgreatly due to oscillation coupling. At the same time, the dots of thespurious oscillations increase in size. Hence, it can be inferred thatthe oscillation intensities increase compared with the mainoscillations. At this time, the main oscillations are deprived of theiroscillation energies by spurious oscillations and so the oscillationintensities of the main oscillations decrease. That is, the resistancevalues of the main oscillations increase.

[0038] The figures are compared. FIG. 6 shows a case where the directionof displacement is made parallel to the direction of the longer sides ofthe blank. The rotational angle Ω about the Y′ axis is −8 degrees. FIG.7 shows a case where Ω is 0, i.e., the direction of the longer sidesdeviates 8 degrees from the direction of displacement at thedouble-rotation cut angle. FIG. 8 shows a case where Ω is 8 degrees andthe direction of the longer sides deviates 16 degrees from the directionof displacement. It can be seen from the comparison of the three figuresthat the frequency shifts are small and spurious oscillations are not sostrong in FIG. 6 where the direction of displacement is parallel to thedirection of the longer sides. However, as can be seen from FIGS. 7 and8, as the deviation from the parallel relation between the direction ofdisplacement and the direction of the longer sides increases, variationwidth of frequency increases, and the oscillation intensity of the wholespurious oscillation increases.

[0039] After checking these facts computationally, oscillators usingcuts of quartz according to the present invention were prototyped underconditions of φ of 20 degrees and θ of 34.0 degrees. Double-rotationcut-angled quartz oscillators of this construction were rotated aboutthe Y′ axis with angles Ω of −8 degrees, 0 degrees, and 8 degrees,respectively. The longer and shorter sides of each blank were madeparallel to the X″ axis and Z″ axis after rotation within the plane. Inthe present prototypes, the longer sides were kept constant. Eachshorter side was varied by varying the Z side ratio from 15.0 to 17.0,and the frequency of the main oscillations of each cut oscillator wasmeasured.

[0040]FIGS. 9, 10, and 11 represent the frequency distributions of theresults of the measurements described above. In FIG. 9, the direction ofdisplacement of the main oscillations is parallel to the direction ofthe longer sides. In FIG. 10, the direction of the longer sides deviates8 degrees from the direction of displacement. In FIG. 11, the deviationis 16 degrees. In FIG. 9, frequency variations are smaller than in FIGS.10 and 11. Also, the variation width increases with increasingdeviation, for the causes considered below. As the deviation from theparallel relation increases, many oscillational couplings with spuriousoscillations occur in various shapes, causing jumps of the frequency ofmain oscillations. Because of these results, it can be seen that astable frequency is obtained irrespective of the shape of the cutoscillator by making the direction of the longer sides parallel to thedirection of displacement.

[0041] The frequency-temperature characteristics of the cut oscillatorsaccording to the invention were measured. The results are shown in FIG.12. A stable frequency of main oscillations can be obtained over a widetemperature range comparable to the frequency-temperaturecharacteristics of the double-rotation oscillator shown in FIG. 3. Ithas been confirmed that rotation about the Y′ axis hardly affects thetemperature characteristics.

[0042] The results above show that in the double-rotation cut-angledoscillator, displacement of the main oscillations is not parallel to thedirection of the longer sides and so coupling with spurious oscillationsexisting thereabout easily occurs. As a result, frequency jumps andresistance value increases occur easily. To avoid them, it is desirableto rotate Ω within the range from −35 degrees to −2 degrees within theplane at the cut angle of double rotation. However, where φ is less than3 degrees, the direction of displacement is almost parallel to thedirection of the longer sides and so in-plane rotation about the Y′ axisis not necessary. Where φ is greater than 30 degrees, the centraltemperature of the temperature characteristic curve becomes too highwith impractical results. Therefore, the range of φ from 3 degrees to 30degrees is desirable. In this range of φ, the range of θ in which thegradient of the tangential line to the temperature characteristic curveis 0 near the central temperature is greater than 33 degrees and lessthan 36 degrees as given by

−35≦Ω≦−2   Equation 2

[0043] wherein, 3.0≦φ≦30

[0044] 33.0≦θ≦36.0

[0045] Especially,

[0046] The relation between φ and Ω that satisfies the function of Eq.(3) shown in FIG. 5 is considered to be the optimum condition. However,the region in which the frequency-temperature characteristics of thedouble-rotation cut oscillator are good differs slightly depending onthe side ratio and on the amount of plateback using the electrodes. Thiscauses a deviation of the optimum region of Ω. Therefore, the width of±3 degrees of the value of the Q derived from Eq. (3) is the optimumregion in practice. This is given by Eq. (4).

Ω°=(−0.0037×φ³+0.1106×φ²−1.161×φ0.239)°  Equation 3

Ω+=(−0.0037×φ³+0.1106×φ²−1.161×φ0.239±3)°  Equation 4

[0047] (wherein, 3.0≦φ≦30)

[0048] The cut of a piezoelectric oscillator (cut of a quartzoscillator) consisting of the quartz plate 12 cut out with the cut angleobtained under the above conditions can be used as a piezoelectricoscillator by hermetically sealing the cut of the oscillator into apackage. FIG. 13 gives explanatory views of the piezoelectricoscillator. FIG. 13(A) is a plan view in cross section taken on line B-Bof FIG. 13(B). FIG. 13(B) is a side elevation in cross section taken online A-A of FIG. 13(A).

[0049] In FIGS. 13(A) and (B), a piezoelectric oscillator 20 has apackage 22 made of an insulating material such as a ceramic material.The package 22 is provided with a cavity 26 accommodating a cut of apiezoelectric oscillator 24. Electrodes 30 and a wiring pattern (notshown) are formed on the bottom surface of the cavity 26 in the package22 to permit electrical connection with external terminals (not shown)formed on the rear surface of the package 22. The cut of thepiezoelectric oscillator 24 is cantilevered and mounted in the cavity26. Specifically, conductive adhesive 32 is applied onto the electrodes30. Connector electrodes 34 of the cut of the piezoelectric oscillator24 are disposed on the adhesive and made stationary. This makes itpossible to electrically energize exciting electrodes 36 of the cut ofthe piezoelectric oscillator 24 from the external terminals on thebottom surface of the package 22. A cover member 38 is mounted on top ofthe package 22, and the inside of the package 22 is maintained as anitrogen ambient or the like.

[0050] The cut of a piezoelectric oscillator according to the presentembodiment can be used as a piezoelectric oscillator by combining thecut of the piezoelectric oscillator with integrated circuit elements andforming an oscillator circuit. For example, a piezoelectric oscillatormodule can be formed by mounting the piezoelectric oscillator 20 shownin FIGS. 13(A) and (C) and integrated circuit elements (not shown) on amodule substrate on which a wiring pattern has been formed. Furthermore,a piezoelectric oscillator package can be fabricated by hermeticallysealing integrated circuit elements into the package 22 shown in FIGS.13(A) and (C) together with the cut of the piezoelectric oscillator 24.

[0051] The cut of a piezoelectric oscillator according to the inventioncan be, for example, planar, convex, or inverted mesa form in which thecentral portion of the cut of the piezoelectric oscillator is recessed.

[0052] Advantages of the Invention

[0053] As described so far, by adopting the cut angle according to thepresent invention, the frequency of the main oscillations can bestabilized irrespective of various shapes of the cuts of quartz.

What is claimed is
 1. A cut of a piezoelectric oscillator comprising: aquartz plate having an electric axis on an X axis, a mechanical axis ona Y axis, and an optic axis on a Z axis, said plate having a sideparallel to an X′ axis established by rotating the X axis in a clockwisedirection about the Z axis within an angle of from about 3 to 30degrees, said quartz plate further having a side parallel to a Z′ axisobtained by rotating the Z axis about the X′ axis in the clockwisedirection within an angle of from about 33 to 36 degrees, wherein thequartz plate has sides parallel to an X″ axis and a Z″ axis,respectively, which have been rotated within angles of from about −35 to−2 degrees in the clockwise direction about the Y axis that is athickness direction of the cut of the piezoelectric oscillator.
 2. A cutof a piezoelectric oscillator as set forth in claim 1, wherein when arotational angle about the Z axis, a rotational angle about the X′ axis,and a rotational angle about the Y′ axis are defined to be φ degrees, θdegrees, and Ω degrees, respectively,Ω°=(−0.0037×φ³+0.1106×φ²−1.161×φ+0.239±3)°  Equation 1 (wherein,3.0≦φ≦30) is satisfied.
 3. A piezoelectric oscillator comprising: thecut of the piezoelectric oscillator as set forth in claim
 1. 4. Apiezoelectric device having a piezoelectric oscillator as set forth inclaim 3.